Mars shows what a woman is attracted to in a man. Being with a man who is strong in her Mars element, or who makes close sextiles with her Mars, makes the relationship much easier, and increases sexual desire and compatibility. For a man, his Mars is part of his masculine nature, so it is best when his partner also relates well with this element.
Mars Inconjunct Neptune
What kind of romantic and sexual relationship do you want? What does your romantic partner desire? The partnership you actually create is based upon both of your ideas about romantic relationships, and in this inconjunct aspect you will feel and think very differently about self assertiveness and sexuality. You will constantly be adjusting your goals to make them more realistic? in terms of your partners opinions. When the Mars person is in the Neptune person, they are likely to feel frustrated because there will be confusion and doubt about what you as a couple really can accomplish.